In the double seat valve known from JP 57-154564A, the first channels join a disc-like deflector in the lower part of the leakage room and in alignment to the second channels in the lower valve disc. On the outer circumference, the deflector has a radial seal that interacts with the internal wall of the leakage room in the statistical state and also during axial movements of the deflector. The deflector is charged in the direction towards the lower valve disc through the spring that supports itself on the upper valve disc. In the upper lift position, the cleaning medium that flows in under pressure is led through a circumferential throttle gap before it flows through the first channels. Out of the first channels, the cleaning medium shoots into the lower part of the leakage room where it impinges on the seal of the lower valve disc with considerable pressure before it flows into the leakage outlet via the second channels. In the lower lift position, the cleaning medium enters the lower part of the leakage room in the leakage room through a throttle gap between the lower valve disc and the deflector and flows out through the second channels. Thereby, cleaning medium also flows through the first channels into the upper part of the leakage room where it impacts on the seal of the upper valve disc with considerable pressure. Thereby, there is the risk of leakages on the seals. Effective cleaning in the area of the radial seal of the deflector is made difficult, even if the radial seal of the deflector performs hauling axial movements along the wall of the leakage room.
In the double seat valve known from DE 10 2007 038 124 A1, a circular ring deflector is connected through spokes to a hub that is guided on a drive rod of the lower valve disc. A slide ring that works together with the wall of the leakage room in a sealing way is disposed in the circumference of the deflector. The deflector should shield the direct incoming flow from the respective seal of a valve disc in a way that the seal is not impinged directly and with a high flow speed by the cleaning medium but that the cleaning medium arrives at the seal essentially without pressure and at a low flow speed in the respective lift position. The sealing slide ring of the deflector can be omitted.
In the double seat valve known from DE 10 2010 046 137 A1, the deflector is guided flexibly on the upper and lower valve discs and equipped with a ring seal on the circumference. In each lift position, radial sealing contact between the deflector and the wall of the leakage room is ensured, which makes flawless cleaning of this area difficult. To avoid too strong impingement of the respective seal of a valve disc in each lift position, the cleaning agent is already throttled during inflow into the leakage room.
In the double seat valve known from U.S. Pat. No. 8,327,881 B2, an external ring of the deflector is connected via spokes to a hub that is guided on a drive rod of the lower valve disc and equipped with a radial seal that seals on the wall of the leakage room. In each lift position, the cleaning medium also impinges with a relatively high pressure on the seal of the valve disc that still has a sealing effect.
Double seat valves that are used for example in the U.S. dairy industry have to comply with the requirements of the PMO, Art. 15p (B) (Pastorized Milk Ordinance). Consequently, no direct impingement through cleaning agent may take place during cleaning of a valve seat on the seal that is opposite to such valve seat, and there may only be atmospheric pressure or negative pressure on the opposite seal if a product waits on such seal. Hence, it needs to be ensured that no cleaning agent leaks through the product line and contaminates the product.